Abstract

The present invention utilizes the modulation ratio between the flicker of a sensor signal and the absolute signal average to detect fire conditions. The system of the present invention requires that the signal on a sensor channel be above a certain threshold and the ratio of the flickering portion of the signal to the absolute signal average be within a certain range. The system may be applied to any sensor signal in response to any source, including, but not limited to, radiation, acoustic or optical signals including ultraviolet, visible or infrared radiation. Signals may be filtered with a median filter to remove noise. A least-mean-square curve-fit is made to the data to account for any growth or decay in the fire signal. The flicker can be calculated using any of several metrics such as standard deviation, p-norms, or maximum deviation, but mean deviation seems to provide optimal performance. The modulation ratio system can be augmented with a separate detection scheme for large-scale fires. The system can also be modified to allow for increased sensitivity in the case of a previous alarm condition. Multi-channel modulation ratio systems may be configured such that each channel's corresponding ratio and absolute signal average must meet the corresponding requirements before a fire alarm is declared. Multi-channel systems may include a form of cross-thresholding wherein the threshold of one channel is dependent upon the signal levels of the other remaining channels.